In four-wheel-drive vehicles, where all of front and rear wheels are drive wheels, there would occur rotating speed differences between the left and right front wheels and between the left and right rear wheels, and thus, it is important to inspect respective drive systems of the vehicles. Heretofore, there have been proposed various methods for inspecting the drive systems of the four-wheel-drive vehicles, such as one disclosed in Japanese Patent No. 4191001 (hereinafter referred to as “the relevant prior patent literature”).
According to the disclosure of the relevant prior patent literature, drive power is transmitted from a front-wheel differential gear, driven directly by an engine, to a rear-wheel differential gear disposed between rear wheels, via a hydraulic clutch and two hydraulic pumps. Further, a one-way clutch for mechanically connecting the rear-wheel differential gear to the front-wheel differential gear at the time of acceleration is attached to the hydraulic clutch.
Further, according to the disclosure of the relevant prior patent literature, a first connecting oil passage is provided to connect between first and second ports, and a second connecting oil passage is provided to connect between third and fourth ports. However, the first connecting oil passage may sometimes be provided to connect between the third and second ports due to an assembly mistake. Thus, there is a need to confirm that the first connecting oil passage is accurately provided to connect between the first and second ports.
Whether the oil passages are connected accurately can be confirmed also by checking behavior of the rear wheels with the vehicle set in a forward traveling state by the engine.
Further, because the one-way clutch is set in a connected or engaged state at the time of acceleration, the drive system including the one-way clutch can be checked by setting the vehicle in a forward traveling acceleration state.
As a result of remarkable enhancement of performance of electric motors in recent years, there have been proposed four-wheel-drive vehicles in which one of the front and rear wheels are driven by an engine while the other of the front and rear wheels are driven by electric motors. One specific example of such four-wheel-drive vehicles will be described with reference to FIG. 7.
As shown in FIG. 7, an electric drive apparatus 100 of the four-wheel-drive vehicle includes: a case 101; a left electric motor 102L (“L” is a suffix indicating “left”); a left sun gear 104L mounted on a left motor shaft 103L; a left planet gear 105L meshing with the left sun gear 104L; a left ring gear 106L surrounding the left planet gear 105L; a left carrier 107L extending from the left planet gear 105L; and a left foot shaft 108L connected to the left carrier 107L and extending through the left motor shaft 103L. The electric drive apparatus 100 also includes: a right electric motor 102R (“R” is a suffix indicating “right”); a right sun gear 104R mounted on a right motor shaft 103R; a right planet gear 105R meshing with the right sun gear 104R; a right ring gear 106R surrounding the right planet gear 105R; a right carrier 107R extending from the right planet gear 105R; a right foot shaft 108R connected to the right carrier 107R and extending through the right motor shaft 103R; brake plates 111 and 112 extending between the left and right ring gears 106L and 106R and the case 101; a hydraulic piston 113 for pressing the brake plate 112; a hydraulic pipe 114 for supplying hydraulic pressure to the hydraulic piston 113; and a hydraulic gauge 115 mounted on the hydraulic pipe 114.
The above-mentioned left sun gear 104L, left planet gear 105L, left ring gear 106L and left carrier 107L together constitute a left planet gear mechanism, an similarly, the above-mentioned right sun gear 104R, right planet gear 105R, right ring gear 106R and right carrier 107R together constitute a right planet gear mechanism. The left planet gear mechanism is a transmission mechanism that places one of the three elements, i.e. left sun gear 104L, left ring gear 106L and left carrier 107L, in a non-rotating state by constraining the one element and the remaining two of the three elements in a rotatable state. More specifically, in the illustrated example of FIG. 8, the left ring gear 106L is placed in the non-rotatable state by the hydraulic piston 113.
Once the left electric motor 102L is activated, the left sun gear 104L rotates, in response to which the left planet gear 105L rotates to revolve along the left ring gear 106L. Then, the left carrier 107L is rotated, so that the left foot shaft 108L is rotated. During that time, hydraulic pressure is continuously applied via the hydraulic pipe 114 to the hydraulic piston 113. However, because a considerable amount of energy is required to generate high hydraulic pressure, continuously applying such high hydraulic pressure to the hydraulic piston 113 as above would increase energy cost.
For the foregoing reason, there exists a need for a sophisticated electric drive apparatus which can reduce necessary hydraulic pressure generating energy. One specific example of such a sophisticated electric drive apparatus will be described below with reference to FIG. 8. As shown in FIG. 8, the electric drive apparatus 100B is characterized by being constructed by adding a one-way clutch 117 to the electric drive apparatus 100 of FIG. 7. The other elements in the electric drive apparatus 100B are similar to those in the electric drive apparatus 100 of FIG. 7 and thus will not be described here to avoid unnecessary duplication.
The one-way clutch 117 is mounted in a given orientation such that it is placed in an engaged state at the time of forward travel of the vehicle and in a disengaged state (free-rotating state) at the other times. When the left electric motor 102L rotates in the forward travel direction, the left ring gear 106L is placed in the non-rotatable state through operation of the one-way clutch 117, and thus, the hydraulic pressure can be set at a zero (“0”) level during that time.
For the electric drive apparatus 100B of FIG. 8, various items are inspected during forward acceleration in the same manner as disclosed in Patent Literature 1. However, because the hydraulic pressure is at the zero (“0”) level during the forward acceleration, it is not possible to inspect the hydraulic pressure, and thus, there is a need to conduct a separate inspection of a hydraulic system by applying hydraulic pressure to the hydraulic piston 113. Therefore, an increased inspection time would be required, which would adversely influence the productivity.
Thus, even with the electric drive apparatus having the one-way clutch incorporated therein, it is required to inspect the hydraulic pressure in parallel with another inspection item, because of a demand for enhanced efficiency of the inspection.